This invention relates to hydraulic cylinders and in particular to constructional details of master cylinders which facilitate their manufacture from plastics material by injection moulding.
Conventionally injection moulded master cylinders include a housing with a bore in which a piston is slideable to pressurise fluid ahead of a main seal on the piston for the supply of pressurised fluid to an outlet, two inlet openings are provided into the bore, a first opening for recuperation of fluid from an associated reservoir to that part of the bore ahead of the main piston seal when the piston is in a retracted position and a second opening placing that portion of the bore between the main piston seal and a second piston seal behind the main seal in permanent communication with the reservoir. Such a master cylinder is hereinafter referred to as xe2x80x9ca master cylinder of the type describedxe2x80x9d.
It is difficult to injection mould a housing of a master cylinder of the type described and in particular the formation of the two inlet openings and the connection with the associated reservoir is problematical resulting in the necessity for the housing to be moulded in two or more parts which must be subsequently secured together either mechanically or by welding or adhesive. This significantly affects the ease and cost of manufacture of the master cylinder housing.
It is an object of the present invention to provide a housing for a master cylinder of the type described which is easier to produce by injection moulding.
Thus according the invention there is provided a housing for a master cylinder of the type described having an external inlet connection formed integrally with the housing, the inlet connection having a free end for direct connection with a conduit connected with the associated reservoir and having a passage for connection with the conduit which opens into the housing bore as the first and second openings, the housing being characterised in that the configuration of the passage and the first and second openings being such that the passage and the first and second openings can be formed by a single moulding core.
The second opening is preferably larger than the first opening to allow the passage of fluid back and forth between the reservoir and the portion of the bore between the main and secondary piston seals with the minimum of restriction to avoid hysteresis in the operation of the master cylinder and to assist in filling of the master cylinder as described hereinafter.
The second opening may be elongate in shape along an axis parallel to the longitudinal axis of the housing.
The invention also provides a method of injection moulding a housing for a cylinder of the type described, the method being characterised by comprising the steps of
injecting plastics material into a mould defining the external shape of the housing including an external inlet connection with a free end for direct connection with a conduit connected with the associated reservoir, said mould having a first core means defining the housing bore and a second core means defining an inlet passage of the inlet connection and the first and second openings;
curing the plastics in the mould;
removing said first and second core means; and,
removing said moulded housing from said mould.
The present invention further provides an hydraulic master cylinder of the type described having a housing of the form described above or produced in accordance with the above described injection moulding method.